基于Lamb波的主动结构健康监测系统研究.doc

华中科技大学
硕士学位论文
基于Lamb波的主动结构健康监测系统研究
姓名:刘洋
申请学位级别：硕士
专业：系统分析与集成
指导教师：王乘
20050507
摘要
经过长期使用土木航空大型管道和大型储物罐等结构中难免会产生大量局部损伤及微裂纹为了使结构和材料处于良好的使用状态必须开发一套科学有效的结构健康监测系统Structural Health Monitoring System简称 SHMSSHMS
可以分为主动 SHMS 和被动 SHMS 两种 被动 SHMS 通过被动传感器进行监测和数据处理仅仅监听通过结构振动产生的信号在主动监测系统中使用附在结构表面或嵌入结构中的激励器和传感器通过激励器激发激励信号在结构中引入弹性应力波利用对传感器的接收信号的分析处理可以有效地探知结构中的损伤情况本文研究在主动 SHMS 中引入 Lamb 波进行探伤这种探伤方式具有探测距离远探伤效率高速度快以及适用的类型比较多等优点具体工作如下
讨论了适合在主动 SHMS 中激励和接收 Lamb 波的激励传感器传统的超声波发生装置体积庞大安装复杂不适合在分布式智能结构中广泛应用而压电晶体激励传感器具有价值低廉体积小质量轻并且抗干扰能力强等优点非常适合在主动 SHMS 中应用
因为 Lamb 波具有多种模式本文通过对 Lamb 波探伤模式的研究分析了利用 A0 模式的 Lamb 波进行单模式探伤代替以往的多模式多次探伤的可行性
根据以上的理论分析构造了利用附在金属板上的压电激励器在结构中产生
A0模式的Lamb波并通过嵌入或附着在结构中的压电传感器进行接收的实验架构
使用 Mindlin 板理论和有限差分法对 Lamb 波传播进行了仿真研究
提出了一种基于 TDOA 模型的损伤定位算法利用该算法可以获得损伤部位坐标的显式表达式计算速度快功耗小并能够对损伤区域的大小做出估计仿 真计算结果和实验结果证明该算法能够提供实时的主动损伤检测同时可以准确快速地对结构中可能存在的单点损伤或者损伤比较集中的区域进行定位和粗略的量化
关键词SHMS, 无损检测， 压电晶体， Lamb 波,Mindlin 板理论 ,TDOA， 损伤定位
IV
Abstract
With paying more and more attention to that the integrity of in—service structures needs to be inspected to determine their physical condition throughout their lifetime， we have discussed active Structural Health Monitoring System (SHMS） using interrogative Lamb waves in this thesis.
SHMS can be either passive or active。 Passive SHMS infers the state of the structure using passive sensors (loading， stress， environmental condition， performance indicators, acoustic emission from cracks, etc.） that are monitored over time and fed back into a structural model. Passive SHMS only “listens” to the structure but does not interact with it. Active SHMS is different from passive SHMS because it uses sensors to interrogate the structure in order to detect damage presence, extent， and intensity。 Active sensors act upon the structure in much the same way that conventional nondestructive evaluation （NDE） transducers do。 Unlike passive sensors (which only listen to the structure)， active sensors interact directly with the structure and find its state of health and reliability. Active SHMS using interrogative Lamb waves would be able to cover large areas from one single location. Such systems would be cost-effective and efficient。
Furthermore， we have discussed the transducers using in SHMS。 Conventional ultrasonic transducers are inappropriate for SHMS applications due to their cost， weight, and size. Conventional ultrasonic transducers could not be embedded in large numbers into a structure without incurring important cost and weight penalties。 For SHMS applications, new types of Lamb—wave transducers such as piezoelectric wafer transducers must be developed, they must be small， light weight, unobtrusive， and low cost.
On the other hand， the key requirements of an advanced SHMS are the ability to detect damaging events， characterize the nature， extent and seriousness of the damages。 In this thesis through discussing the propagation of Lamb waves with Mindlin Plate Theory (MPT) and Finite Difference Algorithm, a damage localization concept using ellipses method is proposed based on the propagation of Lamb waves， which are excited and received by surface—mounted or embedded piezoelectric transducers。 Using the method can provide explicit solutions and can draw a conclusion on the damage area。 Numeric and theory analysis basing on the waves’ difference arrival time of transducers that has been
V